Nicotinic and muscarinic cholinergic receptors are recruited by acetylcholine-mediated neurotransmission within the locus coeruleus during the organisation of post-ictal antinociception

• Tonic and tonic-clonic seizures causes long-lasting antinociception.
• Locus coeruleus pretreatment with atropine decreased the post-ictal antinociception.
• Locus coeruleus pretreatment with mecamylamine decreased the post-ictal antinociception.
• Post-ictal analgesia recruits muscarinic cholinergic receptors of locus coeruleus neurons.
• Post-ictal analgesia recruits nicotinic cholinergic receptors of locus coeruleus neurons.

Post-ictal antinociception is characterised by an increase in the nociceptive threshold that accompanies tonic and tonic-clonic seizures (TCS). The locus coeruleus (LC) receives profuse cholinergic inputs from the pedunculopontine tegmental nucleus. Different concentrations (1 μg, 3 μg and 5 μg/0.2 μL) of the muscarinic cholinergic receptor antagonist atropine and the nicotinic cholinergic receptor antagonist mecamylamine were microinjected into the LC of Wistar rats to investigate the role of cholinergic mechanisms in the severity of TCS and the post-ictal antinociceptive response. Five minutes later, TCS were induced by systemic administration of pentylenetetrazole (PTZ) (64 mg/kg). Seizures were recorded inside the open field apparatus for an average of 10 min. Immediately after seizures, the nociceptive threshold was recorded for 130 min using the tail-flick test. Pre-treatment of the LC with 1 μg, 3 μg and 5 μg/0.2 μL concentrations of both atropine and mecamylamine did not cause a significant effect on seizure severity. However, the same treatments decreased the post-ictal antinociceptive phenomenon. In addition, mecamylamine caused an earlier decrease in the post-ictal antinociception compared to atropine. These results suggest that muscarinic and mainly nicotinic cholinergic receptors of the LC are recruited to organise tonic-clonic seizure-induced antinociception.